The watch is a 136.041 case, probably with an excellent 565 movement. This has a date.
The no date version is the 135.041 which usually has the 552 movement.
Some of the later models have a slightly later movement but the 552/565 are excellent, reliable and easy and comparatively inexpensive to service or source parts for and were used in the rather more sought after Seamaster range of the same era. The movements are ultra reliable. I think that they are great daily wearers which go equally well with suits or jeans and, despite being less expensive or sought after by watch enthusiasts, are still quality Omega watches.
If you do go for a gold plated model, an occasional wipe with a jewellers cloth will remove any tarnish.
I'm a fan of these and own three. In my opinion they look comparatively modern for 60/70s watch, sit slim on the wrist and have a pleasant and pleasing shape. I also think they have a more contemporary wrist presence than many other similarly aged models but that’s probably a matter of taste.
So far as cost is concerned, although Chrono24 is arguably a bit more expensive than eBay and some other options, the information about the watch is generally helpful and if you enter Omega 136.041 or 135.041, you’ll see a decent selection many at a more reasonable price.
You should be able to find a good version, stainless steel or gold plate for around £400-600 but, as
@X350 XJR suggests, read the 'learn to fish' thread. You can always spend a little more if you’re happy with a particular piece.
That said, we all fall in love with watches and often pay more than we should for a particular watch that appeals to us.
Here are a couple of mine with the correct crown although replacement crowns for these models are not difficult to find.
Good hunting
